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An electron-on-helium qubit is a promising physical platform for quantum information technologies. Among all the “blueprints” for the qubit realization, a hybrid Rydberg-spin qubit seems to be a promising one toward quantum computing using electron spins. The main technological challenge on the way to such qubits is a detection of fA range image current induced by a Rydberg transition of a single electron. To address this problem, we aim to use a tank LC-circuit in conjunction with a high-impedance and low power dissipation cryogenic amplifier. Here, we report our progress toward realization of a resonant image current detector with a homemade cryogenic amplifier based on FHX13LG HEMT. We present a detailed characterization of the transistor at room and cryogenic temperatures, as well as details of the amplifier design and performance. At the power dissipation level of amplifier well below 100 μW, the measured voltage and current noise level are 0.6 nV / Hz and below 1.5 fA/ Hz , respectively. Based on the actual image current measurements of the Rydberg transition in a many-electron system on liquid helium, we estimate an SNR = 8 with a measurement bandwidth 1 Hz for the detection of a single-electron transition, providing the noise level at the output is solely determined by the noise of the amplifier.

Photoluminescence (PL) mechanism of carbon quantum dots (CQDs) remains controversial up to now even though a lot of approaches have been made. In order to do that, herein a PL color ladder from blue to near infrared of CQDs with the absolute quantum yields higher than 70% were prepared via a one-pot hydrothermal synthesis route and separated by silica gel column. Time-correlated single photon counting measurements suggest that the electron transition takes in effect in the PL progress of the crystalline core-shell structured CQDs, and the PL properties could be coarsely adjusted by tuning the size of the crystalline carbon core owing to quantum confinement effects, and finely adjusted by changing the surface functional groups consisted shell owing to surface trap states, respectively. Both coarse and fine adjustments of PL, as optical and photoelectrical characterizations and density-functional theory (DFT) calculations have demonstrated, make it possible for top-level design and precise synthesis of new CQDs with specific optical properties.

Liquid‐Phase Transmission Electron Microscopy (LP‐TEM) enables in situ observations of the dynamic behavior of materials in liquids at high spatial and temporal resolution. During LP‐TEM, incident electrons decompose water molecules into highly reactive species. Consequently, the chemistry of the irradiated aqueous solution is strongly altered, impacting the reactions to be observed. However, the short lifetime of these reactive species prevent their direct study. Here, the morphological changes of goethite during its dissolution are used as a marker system to evaluate the influence of radiation on the changes in solution chemistry. At low electron flux density, the morphological changes are equivalent to those observed under bulk acidic conditions, but the rate of dissolution is higher. On the contrary, at higher electron fluxes, the morphological evolution does not correspond to a unique acidic dissolution process. Combined with kinetic simulations of the steady state concentrations of generated reactive species in the aqueous medium, the results provide a unique insight into the redox and acidity interplay during radiation induced chemical changes in LP‐TEM. The results not only reveal beam‐induced radiation chemistry via a nanoparticle indicator, but also open up new perspectives in the study of the dissolution process in industrial or natural settings. In situ Liquid‐Phase Transmission Electron Microscopy observations of the morphological changes of goethite nanoparticles during its dissolution are used to evaluate the influence of radiation on changes in solution chemistry. The results not only reveal beam‐induced radiation chemistry via a nanoparticulate indicator, but also open up new perspectives in the study of dissolution processes in industrial and natural settings.

The optically transparent organic-inorganic terpolymers were obtained on the basis of poly (titanium oxide) and organic monomers of the vinyl series, characterized by the reversible wettability of the surface. The poly (titanium oxide) inside the material had a structure close to anatase and was uniformly distributed over the surface of the sample as it was determined by X-ray phase analysis and electron microscopy. A single-electron transition Ti4++ e ̅ → Ti3+ occurred in the samples under UV-irradiation accompanied by a breaking of the Ti-O bond and a decreasing of the terpolymers transparency from 90% to 20%; the process was reversible in time. The reversible of the samples surfaces from hydrophobic to hydrophilic were observed. The water wetting angle varied within 80 °↔ 5 ° range.

Monolayer graphene has attracted enormous attention owing to its unique electronic and optical properties. However, achieving an effective approach without applying electrical bias for manipulating the charge transfer based on graphene is elusive to date. Herein, we realized the manipulation of excitons’ transition from emitter to the graphene surface with plasmonic engineering nanostructures and firstly obtained large enhancements for photon emission on the graphene surface. The localized plasmons generated from the plasmonic nanostructures of shell-isolated nanoparticle coupling to ultra-flat Au substrate would dictate a consistent junction geometry while enhancing the optical field and dominating the electron transition pathways, which may cause obvious perturbations for molecular radiation behaviors. Additionally, the three-dimensional finite-difference time-domain and time-dependent density functional theory were also carried out to simulate the distributions of electromagnetic field and energy levels of hybrid nanostructure respectively and the results agreed well with the experimental data. Therefore, this work paves a novel approach for tunning graphene charge/energy transfer processes, which may hold great potential for applications in photonic devices based on graphene.

It is shown that in a germanium/silicon nanosystem with germanium quantum dots, the hole leaving the germanium quantum dot causes the appearance of the hole energy level in the bandgap energy in a silicon matrix. The dependences of the energies of the ground state of a hole and an electron are obtained as well as spatially indirect excitons on the radius of the germanium quantum dot and on the depth of the potential well for holes in the germanium quantum dot. It is found that as a result of a direct electron transition in real space between the electron level that is located in the conduction band of the silicon matrix and the hole level located in the bandgap of the silicon matrix, the radiative recombination intensity in the germanium/silicon nanosystem with germanium quantum dots increases significantly.

Understanding the electrode materials’ surface is of fundamental importance for catalytic studies as most electrochemical reactions take place there. Although several operando techniques have been used to monitor the electrocatalytic process, real‐time imaging techniques for observing the surface change on electrode materials are still a challenge and limited to a few stable catalytic systems. Herein, the quasi‐in situ electrochemical transmission electron microscopy (TEM) was carried out to track the morphological and local structure evolution during the oxygen reduction reaction (ORR) on manganese dioxide (MnO2) for the first time. The α‐MnO2 nanorods exhibit comparable ORR electrocatalytic activity (half‐wave potential, E1/2: 0.83 vs. 0.85 V vs. RHE; diffusion‐limiting current density, Jd: −5.46 vs. −5.52 mA cm−2) and better methanol tolerance than Pt/C. An electrochemical TEM chip assembled with a three‐electrode system was used to perform the electrochemical experiments similar to typical testing procedures. The ex situ and quasi‐in situ TEM images consistently showed that MnO2 nanorods had undergone surface roughening, and lattice expansion with 0.97% and 1.97% in the a and c‐axis, respectively as ORR proceeded. The quasi‐in situ electrochemical TEM fills the gap between ex situ characterization and operando spectroscopies and deepens the mechanistic understanding of electrocatalytic processes. The quasi‐in situ electrochemical transmission electron microscopy (TEM) was carried out to monitor the surface morphology and local structure evolution during the oxygen reduction reaction (ORR) process on MnO2 nanorods for the first time. The surface roughened, and the lattice expanded as the ORR proceeded, which was ascribed to ORR electrocatalysis exclusively, evidenced by the comparison between on‐tip and off‐tip.

A quantum-liquid state of spin–orbital-entangled magnetic moments is observed in the 5 d -electron honeycomb iridate H 3 LiIr 2 O 6 , evidenced by the absence of magnetic ordering down to 0.05 kelvin. Honeycomb hosts quantum spin liquid When materials with interacting spins are cooled, magnetic states with long-range ordering usually emerge. However, quantum effects have been predicted to prevent long-range ordering all the way down to temperatures close to absolute zero in materials known as quantum spin liquids, where the term 'liquid' refers to the disordered state of the spins. The realization of such a state in a material with a honeycomb lattice, such as graphene, is expected to also reveal topological excitations. Hidenori Takagi and colleagues demonstrate a quantum-spin-liquid state in the 5 d honeycomb iridate H 3 LiIrO 6 , which shows no magnetic ordering down to 0.05 kelvin. Signatures of unusual excitations suggest that this material is a topological quantum-spin-liquid candidate. The honeycomb lattice is one of the simplest lattice structures. Electrons and spins on this simple lattice, however, often form exotic phases with non-trivial excitations. Massless Dirac fermions can emerge out of itinerant electrons, as demonstrated experimentally in graphene 1 , and a topological quantum spin liquid with exotic quasiparticles can be realized in spin-1/2 magnets, as proposed theoretically in the Kitaev model 2 . The quantum spin liquid is a long-sought exotic state of matter, in which interacting spins remain quantum-disordered without spontaneous symmetry breaking 3 . The Kitaev model describes one example of a quantum spin liquid, and can be solved exactly by introducing two types of Majorana fermion 2 . Realizing a Kitaev model in the laboratory, however, remains a challenge in materials science. Mott insulators with a honeycomb lattice of spin–orbital-entangled pseudospin-1/2 moments have been proposed 4 , including the 5 d -electron systems α-Na 2 IrO 3 (ref. 5 ) and α-Li 2 IrO 3 (ref. 6 ) and the 4 d -electron system α-RuCl 3 (ref. 7 ). However, these candidates were found to magnetically order rather than form a liquid at sufficiently low temperatures 8 , 9 , 10 , owing to non-Kitaev interactions 6 , 11 , 12 , 13 . Here we report a quantum-liquid state of pseudospin-1/2 moments in the 5 d -electron honeycomb compound H 3 LiIr 2 O 6 . This iridate does not display magnetic ordering down to 0.05 kelvin, despite an interaction energy of about 100 kelvin. We observe signatures of low-energy fermionic excitations that originate from a small number of spin defects in the nuclear-magnetic-resonance relaxation and the specific heat. We therefore conclude that H 3 LiIr 2 O 6 is a quantum spin liquid. This result opens the door to finding exotic quasiparticles in a strongly spin–orbit-coupled 5 d -electron transition-metal oxide.

Contact-electrification is a universal effect for all existing materials, but it still lacks a quantitative materials database to systematically understand its scientific mechanisms. Using an established measurement method, this study quantifies the triboelectric charge densities of nearly 30 inorganic nonmetallic materials. From the matrix of their triboelectric charge densities and band structures, it is found that the triboelectric output is strongly related to the work functions of the materials. Our study verifies that contact-electrification is an electronic quantum transition effect under ambient conditions. The basic driving force for contact-electrification is that electrons seek to fill the lowest available states once two materials are forced to reach atomically close distance so that electron transitions are possible through strongly overlapping electron wave functions. We hope that the quantified series could serve as a textbook standard and a fundamental database for scientific research, practical manufacturing, and engineering. The mechanism of contact electrification remains a topic of debate. Here, the authors present a quantitative database of the triboelectric charge density and band structure of many inorganic materials, verifying that contact electrification between solids is an electron quantum transition effect.

Low-temperature measurements proved the existence of a two-dimensional electron gas at defined dislocation arrays in silicon. As a consequence, single-electron transitions (Coulomb blockades) are observed. It is shown that the high strain at dislocation cores modifies the band structure and results in the formation of quantum wells along dislocation lines. This causes quantization of energy levels inducing the formation of Coulomb blockades.